Method of making a modular off-axis solar concentrator

ABSTRACT

A method of making a solar concentrator may include forming a receiving wall having an elongated wall, a first side wall and a second side wall; attaching the first side wall and the second side wall to a reflecting wall to form a housing having an internal volume with an opening; forming a lip on the receiving wall and the reflecting wall; attaching a cover to the receiving wall and the reflecting wall at the lip to seal the opening into the internal volume, thereby creating a rigid structure; and mounting at least one receiver having at least one photovoltaic cell on the elongated wall to receive solar radiation entering the housing and reflected by the receiving wall, the receiver having an axis parallel with a surface normal of the photovoltaic cell, such that the axis is disposed at a non-zero angle relative to the vertical axis of the opening.

CLAIM FOR BENEFIT OF PRIOR-FILED NON-PROVISIONAL APPLICATION

This application is a divisional of, and under 35 U.S.C. §120 claims thebenefit of, U.S. Ser. No. 12/632,268 filed Dec. 7, 2009.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The inventions disclosed herein were made with the support of thegovernment of the United States pursuant to contract numberDE-FC36-07G017052 awarded by the Department of Energy. Therefore, thegovernment of the United States may have certain rights in the disclosedinventions.

TECHNICAL FIELD

The present patent application relates to concentrating photovoltaicsolar power systems and, more particularly, to solar concentratorshaving a modular housing, wherein the primary optical elements are atleast partially defined by the modular housing.

BACKGROUND

Photovoltaic solar concentrators typically are used to generateelectrical power by concentrating sunlight onto photovoltaic devices,thereby collecting sunlight from a large area and concentrating it on arelatively small area of solar cells. Therefore, high efficiency solarcells, such as gallium arsenide-based (“GaAs”) solar cells, may be usedin place of less efficient silicon solar cells, thereby producing moreenergy per unit area and, potentially, at a reduced cost.

Solar concentrators may be configured in various ways and typicallyinclude only refracting optics, only reflecting optics or any reasonablecombination of refracting and reflecting optics. Regardless of theconcentrating optics used, excess heat must be managed at the solar celland the solar cell must be protected from the environment. Therefore,the design process generally requires a compromise between the thermaland/or protective features.

Furthermore, efficient operation of solar concentrators requires precisealignment of the optical elements with the solar cells. Indeed, a moreprecise alignment enables a higher degree of optical concentration,thereby reducing the aggregate solar cell cost. However, prior art solarconcentrator designs typically require costly manufacturing steps toachieve precise alignment, while others sacrifice precision, andtherefore efficiency, to reduce manufacturing costs.

Accordingly, there is a need for a solar concentrator that preciselyaligns the primary optical elements with the solar cells in an off-axisconfiguration, while providing the solar cells with the requisitethermal and environmental protections.

SUMMARY

In one aspect, the disclosed method of making a solar concentrator mayinclude forming a receiving wall from a polymeric material with areflective material incorporated therein for protection from exposure toconcentrated sunlight, the receiving wall having an elongated wall, afirst side wall extending from a first end of the elongated wall, and asecond side wall extending from a second end of the elongated wall;forming a reflecting wall from an optically clear material and having aparabolic contour; attaching the receiving wall to the reflecting wallto form a housing having an internal volume with an opening into theinternal volume, the opening having a vertical axis, such that the firstside wall and the second side wall of the receiving wall are connectedto the reflecting wall; forming a lip on the receiving wall and thereflecting wall; attaching a cover to the receiving wall and thereflecting wall at the lip to seal the opening into the internal volume,thereby creating a rigid structure; and mounting at least one receiverhaving at least one photovoltaic cell on the elongated wall of thereceiving wall to receive solar radiation entering the housing throughthe opening and reflected by the receiving wall, the receiver having anaxis parallel with a surface normal of the photovoltaic cell, such thatthe axis is disposed at a non-zero angle relative to the vertical axisof the opening.

In another aspect, the disclosed method of making a solar concentratormay include forming a receiving wall from a polymeric material with areflective material incorporated therein for protection from exposure toconcentrated sunlight, the receiving wall having an elongated wall, afirst side wall extending from a first end of the elongated wall, and asecond side wall extending from a second end of the elongated wall;forming a reflecting wall from an optically clear material, the primarywall having a parabolic contour and defining a plurality of primaryoptical elements; forming a modular housing by attaching the first sidewall and the second side wall of the receiving wall to the reflectingwall to define an elongated trough having an internal volume with anopening into the internal volume, the opening having a vertical axis;forming an upper lip on the elongated housing surrounding the openinginto the internal volume; providing a cover attached to the receivingwall and the reflecting wall at the upper lip to seal the opening intothe internal volume, thereby creating a rigid structure; and mounting anarray of receivers on the elongated wall to receive solar radiationentering the housing through the opening and reflected by the pluralityof primary optical elements, each receiver of the array of receivershaving an axis parallel with a surface normal of the receiver, such thatthe axis is disposed at a non-zero angle relative to the vertical axisof the opening.

In yet another aspect, the disclosed method of making a solarconcentrator may include forming a housing consisting of a receivingwall and a reflecting wall, the reflecting wall having a plurality ofparabolic optical elements formed as an array of parabolic contours inthe reflecting wall, the receiving wall and the reflecting wall togetherdefining an internal volume, the housing having an opening into theinternal volume; providing the receiving wall with an elongated wall,the receiving wall including a first end and a second end, a first sidewall extending from the first end and a second side wall extending fromthe second end, the first side wall and the second side wall connecteddirectly to the reflecting wall, the receiving wall and the reflectingwall defining a lip; mounting a plurality of receivers on the receivingwall positioned to receive solar radiation entering the housing throughthe opening and reflected by the receiving wall, the plurality ofreceivers each receiving incoming sunlight from the plurality ofparabolic optical elements; and connecting a cover to the lip to sealthe opening into the internal volume, thereby creating a rigid structurethat ensures proper optical alignment between the receiving wall and thereflecting wall, the cover secured to the lip by a selected one ofadhesives, tape, and mechanical fasteners.

Other aspects of the disclosed solar concentrator and method of making asolar concentrator will become apparent from the following description,the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded front perspective view of one aspect of thedisclosed solar concentrator;

FIG. 2 is a top perspective view of the solar concentrator of FIG. 1,shown in a partially assembled configuration;

FIG. 3 is a bottom perspective view of the solar concentrator of FIG. 2;

FIG. 4 is a top plan view of the solar concentrator of FIG. 1, shown ina fully assembled configuration;

FIG. 5 is a side elevational view, in section, of the solar concentratorof FIG. 4;

FIG. 6A is a side elevational view, in section, of a portion of thereflecting wall of the solar concentrator of FIG. 5 in accordance with afirst implementation of the disclosure; and

FIG. 6B is a side elevational view, in section, of a portion of thereflecting wall of the solar concentrator of FIG. 5 in accordance with asecond implementation of the disclosure.

DETAILED DESCRIPTION

As shown in FIG. 1, one aspect of the disclosed solar concentrator,generally designated 10, may include a housing 12 and an array ofreceivers 14, 16, 18, 20, 22, 24 supported by the housing 12. Thehousing 12 may be a modular housing comprised of a receiving wall 26, areflecting wall 28 and, optionally, a cover 30. The receiving wall 26,the reflecting wall 28 and the cover 30 may be assembled and connectedtogether, e.g., with mechanical fasteners, adhesives and/or welds, todefine an internal volume 32. The internal volume 32 may be fullyenclosed by the housing 12.

The receiving wall 26 may include an elongated wall 34 that supports thereceivers 14, 16, 18, 20, 22, 24, and that includes a first end 36 and asecond end 38. A first side wall 40 may extend from the first end 36 ofthe elongated wall 34 and a second side wall 42 may extend from thesecond end 38 of the elongated wall 34. The receiving wall 26 may beformed from a polymeric material, such as polyethylene, polycarbonate oracrylic, using an injection molding process or a vacuum forming process,as is well known in the art. Alternatively, the receiving wall 26 may beformed from sheet metal using a deep draw, stamping process plus a breakform process.

In the event that the receiving wall 26 is formed from a polymericmaterial, the receiving wall 26 may be protected from exposure toconcentrated sunlight. In one example, a metallic, reflective lightshield (not shown) may be positioned on the inside surface of thereceiving wall 26 proximate the receivers 14, 16, 18, 20, 22, 24. Inanother example, a highly reflective material, such as titanium dioxide,may be incorporated into the polymeric material that forms the receivingwall 26.

Furthermore, the wiring (not shown) within the housing 12 may beprotected from exposure to concentrated sunlight. In one example, thewiring may be positioned behind a light shield. In another example, thewiring may be bare or may be coated with a light resistant material,such as ceramic cloth or polymer loaded with a reflective material(e.g., titanium dioxide).

As shown in FIG. 1, the reflecting wall 28 may be elongated and mayinclude an internal surface 44 and an external surface 46. Optionally,the reflecting wall 28 may be constructed from multiple separatesegments that have been connected together. As shown in FIG. 2, thereflecting wall 28 may be connected to the receiving wall 26 to definean elongated trough having an upper lip 48 surrounding an opening 50into the internal volume 32 of the housing 12. Like the receiving wall26, the reflecting wall 28 may be formed from a polymeric material usingan injection molding process or a vacuum forming process, or from sheetmetal using a deep draw, stamping process plus a break form process.

In accordance with a first aspect, the reflecting wall 28 may defineprimary optical elements 52, 54, 56, 58, 60, 62. The primary opticalelements 52, 54, 56, 58, 60, 62 may be sized, shaped and sufficientlyreflective to receive incoming sunlight and direct the incoming sunlightto the associated receivers 14, 16, 18, 20, 22, 24. Those skilled in theart will appreciate that the overall size, shape and geometry of theprimary optical elements 52, 54, 56, 58, 60, 62 may depend on theoverall size and shape of the housing 12, as well as the positioning ofthe receivers 14, 16, 18, 20, 22, 24 within the housing 12, among otherthings.

In one specific aspect, the primary optical elements 52, 54, 56, 58, 60,62 defined by the reflecting wall 28 may be sized, shaped andsufficiently reflective to receive incoming sunlight and focus theincoming sunlight onto the associated receivers 14, 16, 18, 20, 22, 24,as shown by the arrows B₁, B₂, B₃ in FIG. 5. For example, as shown inFIGS. 2, 3 and 5, the primary optical elements 52, 54, 56, 58, 60, 62may be formed as an array of parabolic contours in the reflecting wall28.

Referring to FIG. 6A, in a first implementation of the first aspect, theprimary optical elements 52, 54, 56, 58, 60, 62 defined by thereflecting wall 28 may be rendered reflective by coating the externalsurface 46, or at least a portion of the external surface 46, of thereflecting wall 28 with a layer 66 of reflective material. Optionally, aprotective overcoat layer 68 may be positioned over the reflective layer66 to minimize oxidation and other environmental effects. In accordancewith the first implementation, the reflecting wall 28 may be constructedfrom a material that is sufficiently optically clear, such as clearacrylic, such that incoming sunlight may pass through the reflectingwall 28 before being redirected by the reflective layer 66.

Referring to FIG. 6B, in a second implementation of the first aspect,the primary optical elements 52, 54, 56, 58, 60, 62 defined by thereflecting wall 28 may be rendered reflective by coating the internalsurface 44, or at least a portion of the internal surface 44, of thereflecting wall 28 with a layer 70 of reflective material.

Those skilled in the art will appreciate that the reflective layers 66,70 of the reflecting wall 28 may be formed using various techniques,including optical coatings (e.g., mirror coatings), films, decals or thelike. For example, silver-based, aluminum-based, gold-based orplatinum-based mirror coatings may be used, and may be deposited usingvarious known techniques, such as ion-assisted deposition or sputtering.A specific example of a commercially available reflective material thatmay be used for layer 66 or layer 70 is ECI #800P mirror coating forplastic optical components, available from Evaporated Coatings, Inc. ofWillow Grove, Pa.

In accordance with a second aspect, the reflecting wall 28 may becontoured to support separate optical elements (not shown), such asparabolic glass mirrors. The overall size and shape of the reflectingwall 28 may be formed such that the reflecting wall 28 receives andsupports the separate optical elements in precise alignment with thereceivers 14, 16, 18, 20, 22, 24. In one example, various tabs, clipsand/or detents may be used to ensure proper positioning and alignment ofthe separate optical elements in the housing 12. In another example, asnap-fit-type connection between the reflecting wall 28 and the separateoptical elements may be used. In yet another example, an adhesive, tapeor fused connection between the reflecting wall 28 and the separateoptical elements may be used.

As shown in FIG. 4, the cover 30 may be connected to the lip 48 definedby the receiving wall 26 and the reflecting wall 28 to seal the opening50 (FIG. 2) into the internal volume 32 of the housing 12, therebycreating a rigid structure that ensures proper optical alignment betweenthe receiving and reflecting walls 26, 28. The cover 30 may be securedto the lip 48 of the housing 12 by adhesives, tape (e.g., double-sidedtape) or mechanical fasteners. Optionally, a gasket (not shown) may bepositioned between the cover and the lip 48 to ensure a water-tight sealtherebetween. The cover 30 may be a generally planar sheet oftransparent or partially transparent material. In one example, the cover30 may be formed from a polymeric material, such as polycarbonate oracrylic, or a combination of polymeric materials. In another example,the cover 30 may be formed from glass, and may be attached to the lip 48in a design consideration that compensates for mismatch in thermalcoefficients of expansion between dissimilar materials. Thetransparency, flexibility and weatherability of the material (ormaterials) used to form the cover 30 may be selected based upon designconsiderations.

Still referring to FIG. 4, the receivers 14, 16, 18, 20, 22, 24 may bemounted on, and may extend in a row across, the elongated wall 34 of thereceiving wall 26. While six receivers 14, 16, 18, 20, 22, 24 are shown,those skilled in the art will appreciate that solar concentrators may beconstructed with fewer or more receivers without departing from thescope of the present disclosure.

Referring now to FIG. 5, each receiver 14, 16, 18, 20, 22, 24 (onlyreceiver 14 is shown in FIG. 5) may include one or more photovoltaiccells 72, a secondary optical element 74 (e.g., a lens) and a heat sink76. If a cover 30 will not be used, then the photovoltaic cells 72 andthe secondary optical element 74 may be sealed from the environment in aprotective housing (not shown) or the like. The photovoltaic cells 72may be any cells capable of converting light into electrical energy,such as silicon solar cells, GaAs solar cells or the like. The secondaryoptical elements 74 may focus harvested light, particularly lightdirected to the receivers 14, 16, 18, 20, 22, 24 by the primary opticalelements 52, 54, 56, 58, 60, 62, onto the photovoltaic cells 72. Theheat sink 76 may be any device capable of dissipating heat from thephotovoltaic cells 72. In one example, the heat sink 76 may be a passiveheat sink, such as a fanned heat sink, a heat pipe or the like. Inanother example, the heat sink 76 may be an active heat sink, such as anactive cooling link with a moving heat transfer working fluid.

The receivers 14, 16, 18, 20, 22, 24 may be positioned on the receivingwall 26 such that a vertical axis C (i.e., an axis parallel with asurface normal of the photovoltaic cell) of the receivers 14, 16, 18,20, 22, 24 is at a non-zero angle relative to the vertical axis A of thehousing 12. Without being limited to any particular theory, it isbelieved that the off-axis configuration of the receivers 14, 16, 18,20, 22, 24 may limit or prevent the obstruction of light (arrows B₁, B₂,B₃) entering the housing 12, and also provide for easier maintenance ofthe system.

In one aspect, the non-zero angle between the vertical axis C of thereceivers 14, 16, 18, 20, 22, 24 and the vertical axis A of the housing12 may be about 20 to about 80 degrees. In another aspect, the non-zeroangle between the vertical axis C of the receivers 14, 16, 18, 20, 22,24 and the vertical axis A of the housing 12 may be about 40 to about 70degrees. In yet another aspect, the non-zero angle between the verticalaxis C of the receivers 14, 16, 18, 20, 22, 24 and the vertical axis Aof the housing 12 may be about 50 to about 60 degrees. In yet anotheraspect, the non-zero angle between the vertical axis C of the receivers14, 16, 18, 20, 22, 24 and the vertical axis A of the housing 12 may beabout 55 degrees.

Optionally, the solar concentrator 10 may include brackets or the like(not shown) connected to the housing 12 such that the solar concentrator10 may be mounted to a solar tracker (not shown) or as part of a largersolar array comprised of multiple solar concentrators which would thenbe mounted to a solar tracker. The solar tracker may be configured torotate the solar concentrator 10 such that the vertical axis A (FIG. 5)of the solar concentrator 10 is aligned with the sun as the sun movesacross the sky.

Accordingly, the disclosed solar concentrator 10 has the advantages of afull enclosure and an off-axis configuration and, using advancedmanufacturing techniques (e.g., plastic forming techniques), can bequickly and cost-effectively constructed using relatively few parts.Manufacturing costs and efficiencies (e.g., fewer parts to assembly) canbe even further improved by incorporating the primary optical elements52, 54, 56, 58, 60, 62 directly into the reflecting wall 28 of thehousing 12 using, for example, optical mirror coatings. For example, ahousing of the disclosed solar concentrator may be constructed fromthree parts, and the three parts may be self-fixturing to automaticallyalign the optical elements.

Although various aspects of the disclosed solar concentrator have beenshown and described, modifications may occur to those skilled in the artupon reading the specification. The present application includes suchmodifications and is limited only by the scope of the claims.

What is claimed is:
 1. A method of making a solar concentrator, themethod comprising: forming a receiving wall from a polymeric materialwith a reflective material incorporated therein for protection fromexposure to concentrated sunlight, the receiving wall having anelongated wall, a first side wall extending from a first end of theelongated wall, and a second side wall extending from a second end ofthe elongated wall; forming a reflecting wall from an optically clearmaterial and having a parabolic contour; attaching the receiving wall tothe reflecting wall to form a housing having an internal volume with anopening into the internal volume, the opening having a vertical axis,such that the first side wall and the second side wall of the receivingwall are connected to the reflecting wall; forming a lip on thereceiving wall and the reflecting wall; attaching a cover to thereceiving wall and the reflecting wall at the lip to seal the openinginto the internal volume, thereby creating a rigid structure; andmounting at least one receiver having at least one photovoltaic cell onthe elongated wall of the receiving wall to receive solar radiationentering the housing through the opening and reflected by the receivingwall, the receiver having an axis parallel with a surface normal of thephotovoltaic cell, such that the axis is disposed at a non-zero anglerelative to the vertical axis of the opening.
 2. The method of claim 1,wherein forming the receiving wall includes forming the receiving wallfrom a polymeric material selected from polyethylene, polycarbonate,acrylic, and combinations thereof.
 3. The method of claim 1, whereinforming the reflecting wall includes forming the reflecting wall from apolymeric material selected from polyethylene, polycarbonate, acrylic,and combinations thereof.
 4. The method of claim 1, wherein forming thereceiving wall includes forming the receiving wall with the reflectivematerial including titanium dioxide.
 5. The method of claim 1, furthercomprising mounting a light shield on an inside surface of the receivingwall.
 6. The method of claim 1, further comprising forming the coverfrom a material selected from a polymeric material and glass.
 7. Themethod of claim 1, further comprising securing the cover to the lip by aselected one of adhesives, tape, mechanical fasteners, and combinationsthereof.
 8. The method of claim 1, forming the reflecting wall includesforming the reflecting wall to define at least one primary opticalelement having the parabolic contour.
 9. The method of claim 8, whereinforming the reflecting wall to define at least one primary opticalelement includes forming the reflecting wall to define at least oneprimary optical element having the parabolic contour.
 10. The method ofclaim 1, wherein forming the reflecting wall includes forming thereflective wall by layering a reflective material on an internal surfacethereof.
 11. The method of claim 1, wherein forming the reflecting wallincludes forming the reflecting wall by layering a reflective materialon an external surface thereof.
 12. The method of claim 1, whereinforming the reflecting wall includes coating a reflective material on anexternal surface thereof such that sunlight entering the internal volumepasses through the reflecting wall and is reflected by the coating backthrough the reflecting wall into the internal volume to the receiver,and wherein the reflective material is a mirror coating.
 13. The methodof claim 1, wherein mounting at least one receiver includes providingthe receiver with a lens focused on the photovoltaic cell.
 14. Themethod of claim 1, wherein mounting the at least one receiver includesproviding a heat sink thermally coupled with the photovoltaic cell. 15.The method of claim 1, wherein mounting the at least one receiverincludes disposing the axis of the receiver at a non-zero angle of about20 to about 80 degrees.
 16. A method of making a solar concentrator, themethod comprising: forming a receiving wall from a polymeric materialwith a reflective material incorporated therein for protection fromexposure to concentrated sunlight, the receiving wall having anelongated wall, a first side wall extending from a first end of theelongated wall, and a second side wall extending from a second end ofthe elongated wall; forming a reflecting wall from an optically clearmaterial, the reflecting wall having a parabolic contour and defining aplurality of primary optical elements; forming a modular housing byattaching the first side wall and the second side wall of the receivingwall to the reflecting wall to define an elongated trough having aninternal volume with an opening into the internal volume, the openinghaving a vertical axis; forming an upper lip on the elongated housingsurrounding the opening into the internal volume; providing a coverattached to the receiving wall and the reflecting wall at the upper lipto seal the opening into the internal volume, thereby creating a rigidstructure; and mounting an array of receivers on the elongated wall toreceive solar radiation entering the housing through the opening andreflected by the plurality of primary optical elements, each receiver ofthe array of receivers having an axis parallel with a surface normal ofthe receiver, such that the axis is disposed at a non-zero anglerelative to the vertical axis of the opening.
 17. The method of claim16, wherein forming a reflecting wall includes positioning reflectivematerial on one of an external surface of the reflecting wall or aninternal surface of the reflecting wall.
 18. The method of claim 16,wherein forming the receiving wall and forming the reflecting wall eachincludes forming from a polymeric material using a process selected froman injection molding process and a vacuum forming process.
 19. Themethod of claim 16, wherein forming the receiving wall and forming thereflecting wall each includes forming from sheet metal using a processselected from a deep draw process and a stamping process plus a breakform process.